A transmitter employs beamforming in order to amplify transmitted signals in selected directions, while weakening them in others. To beamform, the transmitter transmits a signal from multiple transmit antennas, but with individually adjusted phase shifts or time delays. This effectively creates a transmit beam in a desired transmit radiation direction of the signal—e.g., through controlled constructive and destructive interference of the phase-shifted signals from individual antenna elements. A transmitter performs a so-called beam sweep in order to determine which of multiple possible transmit beams to use for transmitting to a receiver. The transmitter in this regard transmits known signals on different candidate transmit beams and selects for data transmission whichever of those transmit beams the receiver indicates as being received the best. A typical beam sweep could consist of a set of adjacent beams transmitted one after the other until the entire intended coverage area, e.g. a cell, has been covered.
Correspondingly, a receiver employs beamforming in order to amplify signals received from selected directions while weakening unwanted signals in other directions. The receiver does so by using phase shifts between antenna elements to steer the maximal antenna sensitivity toward a desired direction. This effectively creates a receive beam in the desired direction. A receiver performs a so-called beam scan in order to determine which of multiple possible receive beams to use for receiving from a transmitter. The receiver in this regard receives on different candidate receive beams and selects whichever of those receive beams yields the best receive performance.
A beam sweep or scan improves transmit or receive performance. However, a beam sweep or scan threatens to increase transmit/receive delay, radio resource consumption, energy consumption, and interference due to transmission or reception on multiple beams. This in turn reduces the performance of handover, initial access, or other procedures for which the beam sweep or scan may be performed.
In this document, various terms are used to denote a low-power state in a wireless device, where this state is designed to preserve energy in the wireless device, while still enabling reasonably fast network access, when this is needed. These terms include “idle”, “dormant”, “inactive”, where “idle” may correspond to the RRC_IDLE state in the cellular communication system referred to as Long Term Evolution (LTE) and/or the 5th generation system currently being standardized by the standardization organization 3rd Generation Partnership Project (3GPP), denoted “New Radio” (NR), while “dormant” and “inactive” may correspond to the RRC_INACTIVE state in NR. Correspondingly, the terms “connected” and “active” are used to denote a state of a wireless device, which is designed for active data communication and fast network access. The terms “connected” and “active” may correspond to the RRC CONNECTED state in LTE and/or NR.